I had to resort to flipping this back and forth between Photoshop and Corel Painter, using various grayscale charcoal and graphite brushes. (Mostly in Painter.) Then again, I was curious to try doing this as an actual drawing, as in building my values up from light to dark in layers with strokes of the stylus, as opposed to continuous-tone digital painting. So, I drew & erased with my Intuous 3 Wacom tablet stylus just like using a pencil. (Brushes: Painter's Grainy Cover Pencil, Real 2B and Real 6B pencils.) I mostly used white "chalk" for highlights, but I confess to a little cheater dodge & burn highlighting here and there. That often happens at 2am.
As always, however, it starts with a genuine, honest-to-goodness pencil drawing. (Or should, anyway...) I almost always use a good quality, heavy tracing vellum that I can tape and trace over, refining my sketch as it goes. I always work at least 125-150% of final, printed size. The final version was scanned in at 300 dpi and I saved a clean Photoshop master copy that I could always go back to, if needed. (And I did. Always have a safety net...)
I used layers to separate the foreground art from the background graphics (like the circle, which was built as an ellipse w/ a Triskele embossed fill). But mostly I draw directly into my sketch background, covering and erasing just as if I were using a real piece of illustration board.
The final scanned sketch:
The final 300 dpi grayscale art file, as sent to print, approx. 6" x 10".